Abstract: By making the nonlinear equation group linearized with the spline function, the analytic equation for complex gas pipeline with stable process is established. The equation can express the relationship between flow and pressure at arbitrary location of a pipeline. This analytic method can provide a simple and applied way to systematically analyze the process of complex gas pipe network and to set up the pipeline system's structure. Before analyzing the transient state, the equation can be used to predict and judge the technical parameters of the pipeline network system. The comparison results display a good analogy between the analytic method and SPS analysis software in calculating complex gas pipeline with stable state. The equation is of great value in application especially in the process of pipeline's feasibility study and pipeline design.